Removal of contaminants or impurities from a gas phase stream is a commonly encountered process in petroleum and natural gas processing. For example, many natural gas streams contain at least some CO2 in addition to the desired CH4. Additionally, many refinery processes generate a gas phase output that includes a variety of species, such as CH4 and CO2, that are gases at standard temperature and pressure. Performing a separation on a gas phase stream containing CH4 can allow for removal of an impurity and/or diluent such as CO2 or N2 under controlled conditions. Such an impurity or diluent can then be directed to other processes, such as being directed to another use that reduces the loss of greenhouse gases to the environment.
U.S. Patent Application Publication No. 2008/0282885 describes systems and methods for removing CO2, N2, or H2S using a swing adsorption process. One type of adsorbent that can be used in the swing adsorption process is an 8-ring zeolite, such as a DDR type zeolite.
U.S. Pat. No. 7,255,725 describes a porous inorganic membrane containing carbon and a process for use of such a membrane. A porous carbon-free inorganic membrane (such as a zeolite) is treated with a hydrocarbon-type feed under temperature and time conditions that are suitable for depositing carbon by chemical reaction on the inorganic membrane. The carbon-containing membrane is then maintained at a temperature higher than the deposition temperature for a period of time prior to performing a membrane separation. The membrane is described as being useful for separating non-condensable gases, such as CO2, CH4, or H2, from a hydrocarbon feed.
International Publication No. WO 2006/017557 describes membranes for highly selective separations. After calcination, a molecular sieve membrane such as SAPO-34 is treated with a modifying agent such as ammonia. Such a treated membrane is described as being suitable for improving membrane separation of CO2 from CH4 where the amount of CH4 in a permeate through the membrane is reduced. Other modifying agents are described as silanes and/or amines that react with acid sites of zeolites, and polar compounds such as ethanol.